1. Field of the Invention
The present invention relates to electromagnetic seekers. More specifically, the present invention relates to systems and methods for detecting and tracking targets in clutter.
2. Description of the Related Art
Radio frequency (RF) detection of slowly moving or stationary targets in monostatic clutter is a problem that has recently generated a great deal of interest within the Defense community. Monostatic clutter is naturally produced by ground reflections of the radar""s transmitted signal. Monostatic clutter is thus largest at zero relative Doppler. Monostatic clutter is particularly troublesome when trying to detect slowly moving target, since there is almost no Doppler difference between the clutter and the target. Exemplary targets include surface vehicles, launchers and loitering UAVs (Unmanned Airborne Vehicles). The root of the difficulty lies in the fact that conventional radar systems use Doppler information for detection and tracking functions. As is well-known in the radar art, the Doppler shift is a shift in the frequency of radar returns due to the velocity of the target relative to the velocity of the radar receiver. In the presence of clutter, conventional Doppler radar systems lose the ability to use the target""s Doppler to discriminate it from the clutter. Indeed, the target need not even be nearly stationary for this to be a problem. Even a rapidly moving target can exhibit low Doppler relative to mainlobe clutter if its velocity vector is nearly perpendicular to the velocity vector of the observation platform.
For this reason, most air-to-ground missiles employ either a high-resolution radar seeker or an infrared (IR), electro-optic (EO) or laser-radar based (ladar) seeker. However, the inclusion of these seeker modes increases development and production costs of the host platform. Further, IR seekers exhibit more significant atmospheric limitations (smoke, fog, snow, and/or rain, etc.).
While a number of hardware solutions have been proposed, a need remains for an RF based solution that would provide the basis for an all-weather, dual-mission RF seeker, viz, detection/radar-parameter-estimation performance with respect to both stationary and nonstationary targets, to significantly extend the capability of currently fielded hardware. More specifically, there is a need in the art for a more effective system or method for detecting targets in clutter without relying on a Doppler shift calculation.
The need in the art is addressed by the system and method for detecting a target of the present invention. The inventive method includes the steps of receiving a complex return signal of an electromagnetic pulse having a real and an imaginary component; extracting from the imaginary component information representative of the phase component of the return signal; and utilizing the phase component to detect the target. Specifically, the phase components are those found from the complex range-Doppler map.
More specific embodiments further include the steps of determining a power spectral density of the phase component of the return signal; performing a cross-correlation of power spectral density of the phase component of the return signal between different antenna-subarray (quadrant channels); and averaging the cross-correlated power spectral density of the low frequency components. In an alternative embodiment, the cross-correlation is performed on the phase component of the range-Doppler map directly. This signal can then be averaged to potentially provide improved detection of targets. The cross-correlations of the power spectral densities derived from the complex valued range-Doppler map are then used to detect the target in the presence of monostatic clutter.
An additional teaching providing by the present invention relates to a utilization of the phase component to ascertain a direction of the target and thereby effect target tracking as well as target detection.